USMLE Step 1 Physiology Review 52 03 Rate, Gradients and Pressure

# USMLE Step 1 Physiology Review 52 03 Rate, Gradients and Pressure

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### Begin 52 03 Rate, Gradients and Pressure Transcription

Back to some more questions about basic principles in physiology.  We’ll talk about rate.  Rate is an important concept in physiology.  Rate indicates a quantitative relationship between two entities by relating a change in one to a unit change in another.

What is the most important base for rate?

• Time

In a rate relationship, what are the three different ways that one entity may vary with another within physiology limits?  List them alphabetically.

• First, directly. Second, exponentially. Third, inversely.

Student Doctor, please pause the tape and summarize the information discussed thus far on rate.

• Rate indicates a quantitative relationship between two entities by relating a change in one to a unit change in another.  Time is the most important base for rate.  In a rate relationship, one entity may vary with another directly, exponentially or inversely.

• A gradient is the uneven distribution of mass or energy.

What does it mean to move up gradient or against a gradient?  Let’s say up a concentration gradient?

• This would be proceeding from a point of low concentration to a point of higher concentration.

Given active and passive processes, what processes proceed down gradients and are equilibrium seeking?

• Passive processes.

Blood flows, ions diffuse, and heat is transferred down gradients.  Movement down gradients dissipates heat and the system becomes less organized.  In other words, what increases with movement down a gradient?

• Entropy increases

Much of the work of the body is to develop and maintain gradients.  What kind of gradients propel liquids and semisolids?

Okay now we’ll talk a bit about pressure.

Define Pressure.

• Pressure is defined as force per unit area.

What is the primary unit of measure for pressure?

• Millimeters of Mercury

What is the standard unit of measure for pressure?

• Dynes per square centimeter